Low temperature sputter deposition of Ba 0.96 Ca 0.04 Ti 0.84 Zr 0.16 O 3 thin films on Ni electrodes
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Low temperature sputter deposition of Ba0.96Ca0.04Ti0.84Zr0.16O3 thin films on Ni electrodes N. Cramer, Elliot Philofsky, Lee Kammerdiner and T. S. Kalkur1 Applied Ceramics Research, Colorado Springs, Colorado, 80919 1 Department of Electrical and Computer Engineering, University of Colorado at Colorado Springs, Colorado Springs, Colorado, 80933 ABSTRACT The integration of high-K materials, such as ferroelectrics in the paraelectric state, in integrated circuits presents several challenges. If high-K materials are deposited on-chip after or between Al metalization steps, then these challenges include limits on processing gas composition, deposition temperature and electrode material. Specifically, the atmosphere present during deposition and annealing must be oxygen-free; the deposition and annealing temperatures must not exceed 450 ºC; and the electrode material must be etchable with chemical techniques. We studied rf magnetron sputtered Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) with Ni electrodes because this system meets all the above requirements. The BCTZ deposition process uses pure Ar as the sputter gas and a substrate temperature of 450 ºC. Subsequent anneals may be performed in a reducing (forming gas) atmosphere with little effect on either the dielectric constant or leakage current. The Ni electrodes provide a good substrate for BCTZ films and are much easier to integrate than Pt films. Observed values for the relative dielectric constant K, exceeding 100, were not as high as for BCTZ films on Pt electrodes, however these values are sufficient to provide a clear advantage over other, non-ferroelectric materials. Overall, the device characteristics observed prove that the Ni/BCTZ/Ni capacitor is a valuable technology for on-chip capacitor applications. INTRODUCTION High-K ferroelectric materials continue to be of great interest for a wide variety of on-chip applications. Most studies of integration of these materials have focused on deposition of the ferroelectric prior to any metalization steps. This allows flexibility in the process temperature and in the process gases used. In studies of thin film ferroelectrics in the paraelectric state, the most widely studied material is Ba1-xSrxTiO3 (BST) on Pt electrodes. Deposition of BST has been performed with nearly every possible technique, including MOCVD [1], rf magnetron sputtering [2], pulsed laser deposition (PLD) [3], and sol-gel [4]. The related material, Ba1-xCaxTi1-yZryO3 (BCTZ), has been widely studied and applied as a thick film formed by sintering for multi-layer chip capacitors (MLCCs) [5]. BCTZ has been widely used in the discrete capacitor industry due to its high dielectric constant and low leakage current—qualities shared with BST. In contrast, BCTZ is routinely processed in reducing atmospheres such as forming gas, while the dielectric properties of BST are known to degrade sharply with exposure to reducing anneals [6]. This ability of BCTZ to withstand reducing anneals has allowed the use of Ni electrodes with BCTZ in discrete devices, which
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